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Biomedical subjects

L Collet

Publications and source records attributed to L Collet.

At least 73 records · Page 4Linked to original sources
PubMed1996

Development of cochlear active mechanisms in humans differs between gender.

Despite onset of function early during the third term of gestation, the human auditory system demonstrates continued maturation, thought previously to occur primarily at the neural level. The electromotile properties of outer hair cells appear to contribute substantially to hearing sensitivity and frequency selectivity and lead to the generation of otoacoustic emissions (OAEs). This report demonstrates continued development of cochlear active mechanisms (i.e. end-organ level) after onset of cochlear function, as reflected by OAEs. Significant gender differences also are reported, corresponding to recently observed intersex differences in cochlear length and precursory to gender differences observed in the adult.

Cochlea↗
PubMed1996

Functional asymmetry of medial olivocochlear system in humans. Towards a peripheral auditory lateralization.

The aim of this study was to investigate the human peripheral auditory system in either ear to allow comparison of right and left medial olivocochlear inhibition during contralateral ear stimulation with a broad band noise. The efferent system showed a statistically significant greater right-side activity among 44 young subjects. This laterality appeared to be related to the presence of spontaneous otoacoustic emission but not to gender. This efferent asymmetry and the parallel spontaneous otoacoustic emission asymmetry could explain the lateralization of auditory sensitivity, temporary threshold shift and tinnitus.

Acoustic Stimulation↗
PubMed1996

Attention and evoked otoacoustic emissions: attempts at characterization of intersubject variation.

The present study has two aims: to define the visual attention effect on evoked otoacoustic emissions (EOAEs) found in several previous studies: a first experiment sought to determine the conditions necessary to produce such an effect, and found that, neither the complexity nor the duration of the task modified results obtained under attention conditions. The second experiment sought to characterize the great intersubject variation found in most visual attention studies; two possible explanations are discussed: medial efferent system activity, assessed through the recording of otoacoustic emissions, or subject "attention profile" as drawn from a questionnaire.

Acoustic Stimulation↗
PubMed1996

Effect of contralateral acoustic stimulation on the growth of click-evoked otoacoustic emissions in humans.

Input-output (I/O) functions of click-evoked otoacoustic emissions (CEOAEs) were obtained over a 12 dB range for 64 normally hearing adult listeners with and without contralateral broadband noise (BBN). Contralateral acoustic stimulation (CAS) is a convenient way of suppressing responses to ipsilateral stimuli, probably acting via the medial olivocochlear system (MOCS). The present study shows that this contralateral sound suppression of CEOAEs is largest at low stimulus levels. In fact, the curves obtained under CAS approach the curves obtained without CAS as stimulus level rises. I/O slope analysis for the whole study population (n = 64) showed a slight but significant rise in slope with BBN, which may be interpreted as I/O function decompression. A loss of contralateral suppression effect at high ipsilateral stimulus levels was found in both very low and very high amplitude CEOAE subjects, despite the fact that I/O slopes differed between these two groups, whereas rise in slope under contralateral stimulation failed to be found for these same 2 groups of 16 subjects each. These findings clearly indicate that the MOCS is mostly functional at low sound levels, and suggest that the study of CEOAE I/O slope alteration under CAS may help specify one form of MOCS action on cochlear functioning.

Acoustic Stimulation↗
PubMed1996

Contralateral acoustic stimulation induces a phase advance in evoked otoacoustic emissions in humans.

In 28 normal-hearing human subjects, the medial olivocochlear efferent system was activated by contralateral acoustic stimulation which is able to mimic the inhibitory effects of electrical stimulation of the crossed olivocochlear bundle. A first experiment on 16 subjects demonstrated that a contralateral white noise of 35 dB SL was able to induce temporal changes on transiently evoked otoacoustic emissions in response to clicks of 63 dB SPL. These temporal changes consisted of an advance of click-evoked otoacoustic signals in 87% of cases and is referred to as phase-shift effect. The phase advance, quantified using two signal processing methods in both time and frequency domains, was found to be mainly associated with lower frequencies, with a maximal effect at 1.5 kHz and minimal effects around 3.5 and 4 kHz. In a second experiment, carried out on 12 subjects, a negative relationship was found to exist between the ipsilateral stimulation level (level of clicks ranging from 57 to 69 dB SPL) and the phase-shift effect (PSE). Specifically in the range of levels tested (25-45 dB SL), a linear relationship presenting no obvious saturation effect was observed between the contralateral level and the PSE. The PSE was examined in 6 additional subjects exhibiting pathological symptoms; 2 of 3 individuals, who had no contralateral stapedial reflexes unilaterally, showed the PSE whereas this response was reduced or absent in 3 other subjects in the ear with severed efferents associated with a vestibular neurotomy. The integrity of olivocochlear efferents was, therefore, necessary to obtain a full effect, but the absence of stapedial reflex did not prevent the effect from occurring.

Acoustic Stimulation↗
PubMed1996

Involvement of the olivocochlear bundle in the detection of tones in noise.

To investigate the involvement of auditory efferents in hearing-in-noise in humans, olivocochlear bundle (OCB) functioning and detection-in-noise abilities were compared in 30 subjects. OCB function was assessed in terms of contralateral attenuation of evoked otoacoustic emissions (EOAE): i.e., the reduction in EOAE amplitude elicited by a 30-dB SL contralateral broadband noise. Correspondingly, the detection thresholds for 1- and 2-kHz tone pips embedded in 50-dB SPL broadband noise were measured in the same ear as the EOAEs, successively in the presence and in the absence of a 30-dB SL broadband noise in the opposite ear. The shifts in detection threshold induced by the contralateral stimulation could thus be compared to those in EOAEs. The results indicated significant statistical correlations between the contralateral attenuation of EOAEs and (1) the detection threshold of the 2-kHz signal and (2) the contralaterally induced shift in the 1- and 2-kHz thresholds. Furthermore, the correlation between contralaterally induced reduction of EOAE amplitude and contralaterally induced threshold shift was observed only in the group of subjects who had first performed the detection task in the presence of contralateral stimulation. These results, which suggest that OCB is involved in detection of tones in noise in humans, are discussed in relation to previous physiological and behavioral studies of OCB function.

Acoustic Stimulation↗
PubMed1996

Phase delay measurements of distortion product otoacoustic emissions at 2f1-f2 and 2f2-f1 in human ears.

The present study used distortion product otoacoustic emission (DPOAE) latency as a tool to provide information about the generation sites of 2f1-f2 and 2f2-f1 DPOAEs in humans. The DPOAE 2f1-f2 is supposed to be generated near the f2 site, but little is known about the 2f2-f1 DPOAE processing in humans. The present work sought to test several hypotheses as to the possible generation of 2f1-f2 at the f2 site and of 2f2-f1 at the 2f2-f1 site as well as their backward reflection site, by comparing latencies of the two DPOAEs, under appropriate frequency manipulation. The effect of stimulus level was also studied. The latency values were calculated as the phase-lag related to the frequency shift, using the ILO92 software. Amplitudes were lower and latencies shorter for 2f2-f1 than for 2f1-f2. As expected, 2f1-f2 and 2f2-f1 DPOAE latency decreased with increasing stimulus level and frequency. At 70 dB SPL, latencies of DPOAEs with primaries f1 and f2 or f*1 and f*2, chosen so as to obtain 2f*1-f*2 = 2f2 - f1, were identical, whereas at 55 dB SPL the similarities were less obvious, suggesting two different generation processes. The present study suggests that the comparison of several DPOAE components may produce useful information about their processing within the cochlea.

Adult↗
PubMed1996

Spectral and cepstral properties of vowels as a means for characterizing velopharyngeal impairment in children.

This study investigated spectral differences in the phonation of vowels between a group of 21 children with velopharyngeal impairment and a paired control group of 42 subjects. The speech material was composed of the isolated vowels /a/, /i/, and /u/, a sustained vowel /a/, and four vowels included in spoken words: two nasals /in/ and /on/ in "dindon," and two orals /a/ and /o/ in "gâteau." A bottom-up discriminant function analysis indicated that the cepstrum coefficients and the linear-FFT were the most efficient tools in the test to classify the set of children. They were superior to the results obtained with the formant-representation of the vowels. The use of a perceptive scale (barks) did not improve the results. Discrimination over the total group showed percentages lower than those obtained when boys and girls were assessed separately. The best discriminating results were obtained with the /a/ of "gâteau" for the girls and with the isolated /i/ for the boys.

Case-Control Studies↗
PubMed1996

Is perilymphatic pressure altered in tinnitus?

Tinnitus is characterized by the continuous or intermittent auditory perception of various sounds (buzzing, whistling, etc.) in the absence of any external stimulus. Perilymphatic hyperpressure is one of the numerous mechanisms which could hypothetically be involved in tinnitus generation. In the present experiment, perilymphatic pressure was measured indirectly using the tympanic membrane displacement technique. Twenty-five tinnitus patients were investigated at 10, 15 and 20 dB above the acoustic reflex threshold with ipsilateral stimulation. The variables Vi (inward tympanic displacement), Vm (mean tympanic displacement) and their variations according to stimulus level were compared between tinnitus sufferers and age-matched or hearing-matched controls. Tympanic displacement was measured in sitting and supine positions so as to evaluate cochlear aqueduct patency. No systemic changes in response occurred in tinnitus patients, except at a high stimulation level, perhaps due to hearing impairment.

Adult↗
PubMed1996

Ipsilateral ABR with cochlear implant.

Ipsilateral ABR recording technique was developed with the MXM DIGISONIC DX10 cochlear implant, involving, firstly, setting of recording variables with regard to implant and ABR constraints, and, secondly, enhancement of recording quality by signal processing. The resulting recording quality then enabled us to characterize ABR latency, amplitude and wave reproductibility according to stimulus intensity and stimulation site (electrode stimulated). The findings agree with those of the literature on contralateral human and ipsilateral animal studies. Waves III and V amplitude increased with stimulus intensity. Waves III and V latency was insensitive to stimulus intensity or site. ABR quality diminished basally.

Cochlear Implants↗
PubMed1996

A new stimulation strategy for recording electrical auditory evoked potentials in cochlear implant patients.

Recording electrical auditory brainstem responses (EABR) provides clinical insight about responses of the residual post-cochlear neural system to electrical stimulation in profoundly deaf patients. A new strategy is presented for stimulating patients already implanted with a 15-electrode cochlear implant. Since the device is fully re-programmable via a RS-232 PC interface, it was possible to load a specific stimulating strategy designed to improve the spatial locus and the temporal structure of the impulse stimulation. Waves III to V emerge more clearly when this method is applied.

Adult↗
PubMed1995

Evidence of a medial olivocochlear involvement in contralateral suppression of otoacoustic emissions in humans.

Otoacoustic emissions (OAEs) evoked by click stimuli were recorded in both ears of 20 normal human subjects, in the presence and absence of a contralateral masking broad band noise. No difference in the amplitude of OAE suppression was noted between the first tested ear and the second one. In addition, 20 pathological subjects were tested according to the same protocol. Ten of them belonged to a group of patients whose vestibular nerve was sectioned on one side to relieve incapacitating vertigo and thus represented a group in whom olivocochlear efferents were severed. A great reduction of suppression observed in the operated ear suggested that olivocochlear efferent fibers are necessary to obtain a full suppressive effect. Three of the pathological subjects were patients who had undergone a decompression of the facial nerve which necessitated the same surgical approach as vestibular neurotomy, but without any section of vestibular fibers. This surgical control group demonstrated that the surgical act by itself cannot explain the difference observed in the neurotomized group. Finally, seven of the pathological subjects were patients with Bell's palsy, which paralyses the facial nerve and abolishes the stapedial reflex. No suppression difference was observed between healthy ears and ears without stapedial reflex. Therefore, it appeared that the stapedial reflex was not involved in the contralateral suppression of EOAEs. However, as the tensor tympani muscle remained functional in these patients, its involvement in the suppressive effect cannot be excluded.

Adult↗
PubMed1995

Medial olivocochlear system and loudness adaptation: differences between musicians and non-musicians.

Simple loudness adaptation and crossed olivocochlear feedback were investigated--through the Tone Decay Test (TDT) and Transiently Evoked Otoacoustic Emission (TEOAE) recording, respectively--in a sample of normal-hearing subjects including both musicians and non-musicians. The results for musicians and non-musicians differed statistically: the musicians showed on average less loudness adaptation and a greater reduction in TEOAE amplitude under contralateral acoustic stimulation, suggesting a stronger medial efferent feedback on the auditory periphery in these subjects. This finding, that not only psychoacoustic performance but also the physiological mechanism is different in musicians, strongly suggests that the latter should, like the former, be influenced by auditory "training" such as music studies. This perspective is discussed in detail in the text, since it raises puzzling questions and outlined promising issues in the field of auditory psychophysiology.

Audiometry, Pure-Tone↗
PubMed1995

Influence of auditory stimulation and visual attention on otoacoustic emissions.

Transient Evoked otoacoustical Emissions (TEOAEs) express the micromechanical activity of the cochlear outer hair cells (OHCs). The inhibitory effects of contralateral acoustic stimulation and of visual attention tasks on TEOAE amplitude is well-established. Contralateral auditory stimulation and attention affect cochlear micromechanics via the medial olivocochlear efferent system. The present study is a quantitative comparison of the individual and combined effects of these two inhibitory phenomena in the same subjects. TEOAEs were recorded in seven normal-hearing subjects in absence of inhibitory stimulus (S1), under contralateral 95 dB SPL white-noise stimulation (S2), during a visual attention task (S3) and with simultaneous presentation of both forms of stimulus (S4). Significant reductions in TEOAE amplitude were found with contralateral stimulation (S2) and visual attention (S3) (p = 0.01 and 0.05 respectively, in confirmation of previous studies. The inhibitory effect of combined stimulation (S4) was found to be yet more significant (p = 0.004) than the inhibition obtained with each stimulation presented alone.

Acoustic Stimulation↗
PubMed1995

Spontaneous and evoked otoacoustic emissions in pre-term and full-term neonates: is there a clinical application?

In neonates and infants, hearing impairment leads to impaired language and cognitive development. For that reason, early detection of this sensory deficit is of outstanding importance, particularly in pre-term neonates, who constitute a high risk population in regard to very early acquired hearing loss. Evoked (EOAE) and spontaneous otoacoustic emission (SOAE) recording in 93 pre-term and full-term neonates revealed that this technique is potentially useful for auditory screening in neonatology units. EOAEs and SOAEs can be recorded successfully from 30 weeks of conceptional age. SOAEs were found to be prevalent in females and presented higher peak numbers in right than in left ears. Furthermore, SOAE incidence in pre-term and full-term neonates was found to be high in EOAE positive ears, associated with strong and robust EOAEs.

Acoustic Stimulation↗
PubMed1995

Effect of interstimulus interval on evoked otoacoustic emissions.

In order to explore extensively the effect of interstimulus interval, including very short interstimulus intervals, on evoked otoacoustic emissions (EOAEs), several EOAE recordings were carried out using pairs of clicks: a suppressor click preceded the stimulus click generating an EOAE, with various intervals between the two clicks. EOAEs elicited by two clicks separated by intervals under 8-9 ms had significantly smaller amplitudes than EOAEs evoked by the stimulus alone. The amplitude decay correlated with the interclick interval, and was about 40% when the interclick interval decreased from 12 to 1 ms. This phenomenon has been noted before but not precisely quantified. It might reflect an adaptive mechanism within the outer hair cells, which has been previously described, or else mechanical interactions on the basilar membrane. The delay in EOAE decrease is of the same order as the first phase of neural adaptation, known as 'rapid adaptation', and these thus may prove to be correlated.

Acoustic Stimulation↗
PubMed1995

Spontaneous otoacoustic emissions in preterm neonates: prevalence and gender effects.

A number of lines of evidence indicate that the human cochlea is fully functional as a mature sound transducer by 6 months of age. However, information about the development of the active cochlear mechanisms and notably the development of outer hair cell (OHC) activity is yet incomplete. Recording and analysis of otoacoustic emissions (OAEs), probably generated by the OHCs of the organ of Corti, have led to a better understanding, in humans, of how sounds are analysed in the cochlea by means of active mechanisms. Evoked OAEs (EOAEs) and spontaneous OAEs (SOAEs), when they can be recorded in full-term and preterm neonates, show different characteristics from those in adults, suggesting that maturation of the peripheral auditory system is incomplete at birth. To learn more about this maturation, using the best-established facts concerning SOAEs in adults, such as their greater prevalence in females and also in right ears, SOAEs were studied in more detail in 81 preterm neonates, from 30 to 40 weeks of conceptional age, all presenting bilateral EOAEs according to objective criteria. The first finding of this study was that SOAEs existed and could be recorded as of 30 weeks of conceptional age in humans. Some SOAE characteristics in preterm neonates, such as prevalence, peak number and acoustic frequencies, showed similarity with full-term neonates. Comparison of other criteria between the two populations, such as greater SOAE prevalence in right ears and higher SOAE peak number in females, suggested that these developmental factors emerge around term in humans. Comparison of SOAE characteristics between male and female preterms suggested that male preterms were less advanced in peripheral auditory development than were female preterms.

Acoustic Stimulation↗